diff --git a/Common.mak b/Common.mak
index 241a719cd..28e340176 100644
--- a/Common.mak
+++ b/Common.mak
@@ -593,7 +593,7 @@ endif
 
 #### Lunatic development
 # LuaJIT standalone interpreter executable:
-LUAJIT:=luajit
+LUAJIT=luajit$(EXESUFFIX)
 # Options to "luajit -b" for synthesis. Since it runs on Linux, we need to tell
 # the native LuaJIT to emit PE object files.
 ifeq ($(PLATFORM),WINDOWS)
@@ -607,22 +607,10 @@ ifeq ($(PLATFORM),WINDOWS)
 endif
 
 ifneq ($(LUNATIC),0)
-    COMPILERFLAGS+= -Isource/duke3d/src/lunatic -DLUNATIC
     ifneq ($(USE_LUAJIT_2_1),0)
         COMPILERFLAGS+= -DUSE_LUAJIT_2_1
     endif
 
-    # Determine size of _defs*.lua bytecode once.
-    ifndef DEFS_BC_SIZE
-        DEFS_BC_SIZE := $(shell $(LUAJIT) -bg -t h source/duke3d/src/lunatic/_defs_game.lua -)
-        DEFS_BC_SIZE := $(word 3, $(DEFS_BC_SIZE))
-    endif
-    ifndef DEFS_M32_BC_SIZE
-        DEFS_M32_BC_SIZE := $(shell $(LUAJIT) -bg -t h source/duke3d/src/lunatic/_defs_editor.lua -)
-        DEFS_M32_BC_SIZE := $(word 3, $(DEFS_M32_BC_SIZE))
-    endif
-    COMPILERFLAGS+= -DLUNATIC_DEFS_BC_SIZE=$(DEFS_BC_SIZE) -DLUNATIC_DEFS_M32_BC_SIZE=$(DEFS_M32_BC_SIZE)
-
     ifeq ($(PLATFORM),WINDOWS)
         LIBS+= -lluajit
     else
diff --git a/GNUmakefile b/GNUmakefile
index b0060b0e4..9836a1392 100644
--- a/GNUmakefile
+++ b/GNUmakefile
@@ -424,6 +424,19 @@ DUKE3D_EDITOR_MISCDEPS=
 LUNATIC_SRC = $(DUKE3D_SRC)/lunatic
 LUNATIC_LUA_PREFIX = luaJIT_BC_
 ifneq (0,$(LUNATIC))
+    COMPILERFLAGS += -I$(LUNATIC_SRC) -DLUNATIC
+
+    # Determine size of _defs*.lua bytecode once.
+    ifndef DEFS_BC_SIZE
+        DEFS_BC_SIZE := $(shell $(LUAJIT) -bg -t h $(LUNATIC_SRC)/_defs_game.lua -)
+        DEFS_BC_SIZE := $(word 3, $(DEFS_BC_SIZE))
+    endif
+    ifndef DEFS_M32_BC_SIZE
+        DEFS_M32_BC_SIZE := $(shell $(LUAJIT) -bg -t h $(LUNATIC_SRC)/_defs_editor.lua -)
+        DEFS_M32_BC_SIZE := $(word 3, $(DEFS_M32_BC_SIZE))
+    endif
+    DUKE3D_CFLAGS += -DLUNATIC_DEFS_BC_SIZE=$(DEFS_BC_SIZE) -DLUNATIC_DEFS_M32_BC_SIZE=$(DEFS_M32_BC_SIZE)
+
     # Lunatic object base names. These are not used in targets directly.
     LUNATIC_LUA_OBJS = \
         defs_common.lua \